There are a variety of image products such as printers, copiers, and high-value added products of the printers and copiers including a communication function, such as combined machines and commercial printing machines in the market. In image forming methods, there are a variety of methods such as an electro photographic method, an inkjet method, and a thermal method. Also, in a field of production printing, digitalization technology in both a sheet type machine and a continuous business form type machine has been advancing. Recently, products such as the electro photographic type machine and the inkjet type machine have been brought into the market. In view of user's needs, demands for high image quality, personal information assurance and accurate color reproduction has been increasing as multidimensional images, and high-definition and high-density images can be gained by converting black and white print to color print. Also, diversification of service forms provided for the users proceeds, including advertising corresponding to personal preference in high image quality photographic print, brochure print, bill and so on.
As techniques corresponding to a high-quality picture technology, products related to the following techniques have been launched into the market: products that include a concentration sensor to detect toner concentration of an intermediate transcriptional body and a photoreceptor before being firmly fixed, and stabilize a toner supply amount in the electro photographic type; products that take an image of an output image by camera and inspect the image by character recognition or variance detection by a difference between the images without depending on the image forming type in the personal information assurance; and products that output a color patch, measure a color of one or plural points by spectrometer and perform calibration in the color reproduction. These techniques are desirable to be performed for a whole area of the image to respond to image variance between pages or within a page. Examples of evaluation techniques in full width measurement of the image are given as the following.
For example, Japanese Patent Application Publication No. 2008-518218 (which is hereinafter called Patent Document 1) discloses a technique that measures a spectral characteristic of a full width, by lining up plural line-shaped light receiving devices as a detection system and by setting a mechanism to relatively move a measurement object to the detection system. Further, a light shielding wall is set to prevent crosstalk between the light receiving devices by reflected light from the measurement object area.
Moreover, Japanese Patent Application Publication No. 2005-315883 (which is hereinafter called Patent Document 2) discloses a technique that obtains a spectral characteristic of a full width by emitting light continuously from a light source with different light wavelength bands across the full width and by obtaining reflected light.
Furthermore, Japanese Patent Application Publication No. 2002-310799 (which is hereinafter called Patent Document 3) discloses a technique that emits light to a full width of a printing surface, detects a concentration of a certain area by a line sensor camera, averages the concentration and compares the averaged concentration with a reference concentration.
In addition, Japanese Patent Registration Publication No. 3566334 (which is hereinafter called Patent Document 4) discloses a technique that scans a manuscript and a specified manuscript plural times and evaluates a similarity degree of common color information from logical addition processing between images.
Also, Japanese Patent Application Publication No. 2003-139702 (which is hereinafter called Patent Document 5) discloses a technique that emits light to a full width of a printing surface, and obtains a spectral characteristic of the full width by a combination of CCD (i.e., Charge Coupled Device) and either a diffraction grating or a refraction grating.
However, if a color of an image is measured across a full width, the following configurations are considered in general: a configuration that emits plural lights limited in different wavelength bands and takes an image by an area sensor, or relatively moves a measurement system and an object to be inspected, taking an image by a line sensor; and a configuration that sets plural imaging systems and limits wavelength bands of reflected light from the object to be inspected incident on the imaging system. On this occasion, in an image corresponding to plural obtained wavelength bands, if a difference occurs at positions of the object to be inspected between the images, it is impossible to measure color information at each position of the object to be inspected.
Here, as a method that measures the color information from plural images in different wavelength bands, there is a method that compares intensity of the reflected light obtained at the position of object to be inspected of each the images with a reference of an original image or manuscript data. Also, there is a method that estimates a continuous spectral characteristic from the intensity of the reflected light amount obtained at a position of the object to be inspected of each of the images, by applying Winner estimation. Therefore, if a different position is selected as an object to be inspected in each of the images, an error would occur in comparison with the reference or estimation of the continuous spectral characteristic.
The technique disclosed in Patent Document 1 uses the line-shaped measurement system and uses a general configuration that can measure the image color of the object to be inspected across the full width. However, the technique does not include a measure that reduces the position gap of the images obtained at each of the wavelength bands.
The technique disclosed in Patent Document 2 uses a configuration that obtains the reflected light from the object to be inspected by the continuous irradiation light from the light source with different wavelength bands, but it is impossible for the configuration to measure the spectral characteristic of the same position of the object to be inspected because of occurrence of time lag. If the configuration had included plural pairs of the light source and the light receiving system, the positions to be inspected of each of the images in different wavelength bands could have been highly likely shifted.
The technique disclosed in Patent Document 3 also has had a configuration that obtains the color information across the full width, but the technique seems to use a representative value by a process that averages the concentration of the detected area, which cannot ensure color distribution of the object to be inspected.
The technique disclosed in Patent Document 4 determines the similarity degree by comparing the object to be inspected with the manuscript in each of the wavelength bands, but cannot specify color variation of the object to be inspected. Moreover, even if the image is reconstituted from the color information of the individually obtained image, it has been impossible to determine whether the color variation has occurred in an actual object to be inspected.
The technique disclosed in Patent Document 5 has big restrictions in speed to obtain the color information of the image holding medium (e.g., paper) of an object to be read because a reading speed for the line sensor dramatically decreases due to a restriction of a data reading characteristic of the CCD with a two-dimensional pixel structure.